Business Acquisition (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
	Dec. 01, 2014	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	[1]
Business Acquisition [Line Items]
Business combination, indemnification period	2 years
Business combination, preacquisition contingency, amounts released from escrow		$ 1,600	$ 1,600
Assets
Goodwill		142,402	142,402	$ 131,885
GAB Robins
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired	100.00%
Payments to acquire businesses, gross	$ 71,812
Business combination, indemnification assets, amount as of acquisition date	6,329
Amortization of intangible assets		749	1,259
Revenue of acquiree since acquisition date		21,820	$ 38,095
Assets
Cash and cash equivalents	5,735
Accounts receivable	19,182
Unbilled revenues, at estimated billable amounts	7,169
Prepaid expenses and other current assets	7,443
Property and equipment	4,083
Goodwill	14,119
Intangible assets	40,535
Other noncurrent assets	1,933
Deferred income taxes	4,833
Total Assets	105,032
Liabilities
Other current liabilities	22,714
Noncurrent liabilities	4,580
Total Liabilities	27,294
Net Assets Acquired, Before Noncontrolling Interests	77,738
Noncontrolling interests	5,926
Net Assets Acquired, Net of Noncontrolling Interests	$ 71,812
Customer relationships | GAB Robins
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life			18 years
Assets
Intangible assets		$ 38,210	$ 38,210
Minimum | Intangible assets not including customer relationships | GAB Robins
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life			2 years
Maximum | Intangible assets not including customer relationships | GAB Robins
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life			5 years

[1] Derived from the audited Consolidated Balance Sheet